Grassland Water District

Site Description

This station accounts for approximately 19.5% of the total wetland drainage from GWD. Drainage enters Mud Slough (north) from duck clubs located to the north-west of Los Banos. Mud Slough also conveys drainage from the southern division of GWD which is diverted into the Slough via the Santa Fe Canal as well as wetlands served by Rubino Ditch, Mosquito Ditch and Volta Wasteway. Flows at this station range from a high in excess of 100 cfs during the winter after flood-up and after significant rainfall events to less than 2 cfs during the middle of the summer after all remaining seasonal wetlands are drained and summer irrigation has been completed. At the station flow is estimated using a stage-discharge rating as well as with the aid of an acoustic Doppler (SONTEK) transducer. The flow rating is less accurate but provides useful redundancy and is useful during times when the stage drops below the elevation of the SONTEK instrument. This station is subject to regular backwater conditions flowing downstream obstacles and the confluence with Fremont Canal Drain, which occasionally contains moderately high flows. In both cases regular rating of Mud Slough at the gauge site is necessary – in particular after large storms when sediment deposition in the stream bed can occur and during the spring and early summer when the channel is cleared of cattails and accumulated sediment.